docs: def set_field_name(self):
          """Sets the context's ``pending_symbol`` as its ``field_name``."""
          assert self.pending_symbol is not None
          assert not self.value
          self.field_name = _as_symbol(self.pending_symbol, is_symbol_value=False)  # pending_symbol becomes field name
          self.pending_symbol = None  # reset pending symbol
          self.quoted_text = False
          self.line_comment = False
          self.is_self_delimiting = False
          return self